Electrical interactions between a real ventricular cell and an anisotropictwo-dimensional sheet of model cells

We have extended our "coupling clamp" technique, in which we couple a real cell to a real-time simulation of a model cell, to now incorporate a real c ardiac cell as the central element of a two-dimensional sheet of model cell s, in which the coupling conductances may be different in the x: and y dire ctions and a specific region of lack of coupling conductance may serve as a resistive barrier. We stimulated the real cell in the central location and determined the critical size of the real cell for successful activation of the entire sheet. We found that this critical size was decreased when anis otropy was present compared with the isotropic case and was further decreas ed when the central site of stimulation was close to the resistive barrier. The heart normally has some degree of anisotropy, and it has been shown th at the remodeling that occurs in peri-infarction zones produces a particula r loss of lateral connections compared with end-to-end connections among he art cells. We propose that the normal existence of anisotropy and enhanceme nt of the degree of anisotropy both by loss of lateral gap junctions and th e development of resistive barriers may play a facilitating role in the dev elopment of ectopic foci that may lead to cardiac arrhythmias.